This invention relates to rotating magnetic memories.
Rotating magnetic members used as storage media are well known in the form of magnetic drums, magnetic disks, magnetic strips, and flexible magnetic disks. The latter category of rotating magnetic memories offers enhanced volumetric efficiency in the storage of signals; that is, the number of disks stored in a given volumetric unit appears to be a maximal when used with such flexible magnetic disks. Such flexible magnetic disks preferably have a relatively thin, axial dimension in the order of magnitude from 0.0010, or 0.005 inch. It is also preferred, for stabilization purposes, that such disks be axially spaced apart a small distance, such as one-half mil to ten mils, with radial air flow being circumferentially uniformly distributed for stabilizing the individual disks during rotation.
The assembly of such disks is referred to as a flexible disk pack assembly. Each of the disks has at least on record signal receiving portion, such as a magnetic coating. In other embodiments, each disk may have two surfaces for receiving signals. One problem in using such a flexible disk pack assembly is to access such record surface portions in a precise, rapid, and repeatable manner. To position an accessing mechanism between two disks spaced apart on a center-to-center basis of 0.015 inch or less requires accurate positioning devices. Further, because of thermal instabilities in any large apparatus, such as one employing 250 or more such flexible disks, plus tolerance build-up from one end of the pack to the other, it is exceedingly difficult to rapidly locate any selected disks for accessing a given record surface portion.
One solution to the axial positioning problem is shown by Lynott and Masterson in the IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 12, No. 1, June 1969, on Page 81, entitled "Disk Memory." Lynott and Masterson teach that by varying the diameter of the various disks, selection of a given disk is enhanced. According to Lynott and Masterson, one disk has a maximum radius with all of the other disks having succeedingly reduced radii to a minumum radius disk. While this enhances selection, it requires that the disk have a significant change in diameter; hence, the recording surface available for receiving signals on a volumetric basis is not maximized, i.e., the recording surface on the minimum radius disk, when using a large number of disks, is substantially less than a maximum radius disk. Also, the number of indexing points, i.e., for ten disk packs, there are ten different radii, requires ten different radial positions of the accessing mechanism. This complicates the control of an accessing mechanism and, hence, increases cost.
It is desired that a flexible disk pack be constructed such that accessing is enhanced without providing a great difference in radii of the various disk record members.